Due to the rapid depletion of water resources, a study on the system for reprocessing and cleaning contaminated water has been actively conducted. Particularly, in a water processing apparatus such as a water cleaning system, a water mixing apparatus is an essential component for water processing and increases a contact surface between water and oxygen and facilitates the supply of oxygen and thus can maximize the efficiency in reprocessing and cleaning sewage.
Further, if eutrophication causes green or red tide, mass strandings may occur in a fishery or fish farm due to shortage of oxygen supply to creatures in the water. In this case, by mixing water to facilitate the supply of oxygen, such a risk can be suppressed or reduced.
However, a conventional water processing apparatus provides a simple mixing function and thus has a small mixing output, i.e., mixing efficiency, vs. input energy. Therefore, it is difficult to obtain a required effect.
In this regard, Japanese Patent Laid-open Publication No. 2006-062835 (entitled “Propeller, agitating machine, and conveyor”) discloses a configuration in which multiple blades are spirally spaced from one another in line on an outer periphery of a rotary shaft, and a front end in a spiral direction of each of blades is crossed with a rear end in the spiral direction of the adjacent blade going forward and a direction of a shaft center of the rotary shaft.
Further, conventionally, a general mixing apparatus added with an aerating apparatus has been used as a mixing and aerating apparatus, and there is a shortage of consideration of aerating flow.
In other words, in the conventional apparatus, a propeller used in a mixer is also used to perform an aerating function, and this propeller is configured without consideration of two-phase flow in which a liquid and a gas are mixed and thus not optimized.
Therefore, in the conventional mixing and aerating apparatus, the use of the same propeller causes deterioration of the aerating function due to a big difference in driving conditions such as density or the like between single-phase flow in which only a liquid is present as a working fluid for driving the mixer and two-phase flow in which a liquid and a gas are mixed for performing mixing and aerating.